Shape- and scale-dependent coupling between spheroids and velocity gradients in turbulence

Pujara, Nimish; Arguedas-Leiva, José-Agustín; Lalescu, Cristian; Bramas, Bérenger; Wilczek, Michael

doi:10.1017/jfm.2021.543

Cited by 7 publications

(5 citation statements)

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“…2015; Pujara et al. 2019, 2021), pointing out the preferential alignment of sufficiently short fibres with the fluid vorticity and that of longer fibres with the most extensional eigenvector of the strain rate. We note, however, that such theoretical and computational studies still often rely on a one-way coupling assumption and are typically based on the classical Jeffery's model (the latter strictly holding only for fibres shorter than the dissipative length scale).…”

Section: Resultsmentioning

confidence: 97%

“…As the final step of our investigation, we focus on a peculiar issue of anisotropic particles in turbulence (Voth & Soldati 2017) principal directions of the strain rate). The topic has been extensively investigated in the framework of fibres with infinitesimal length, and more recently for finite-size fibres (Pumir & Wilkinson 2011;Ni et al 2015;Pujara et al 2019Pujara et al , 2021, pointing out the preferential alignment of sufficiently short fibres with the fluid vorticity and that of longer fibres with the most extensional eigenvector of the strain rate. We note, however, that such theoretical and computational studies still often rely on a one-way coupling assumption and are typically based on the classical Jeffery's model (the latter strictly holding only for fibres shorter than the dissipative length scale).…”

Section: Preferential Alignmentmentioning

confidence: 99%

“…2021; Pujara et al. 2021) and inertia (expressed by means of a representative Stokes number) (Bounoua, Bouchet & Verhille 2018; Kuperman, Sabban & van Hout 2019).…”

Section: Introductionmentioning

confidence: 99%

“…Focusing on rigid fibres (i.e. rods), numerous efforts have been devoted to describe in detail how such alignment, and consequently the fibre's rotation rate, are qualitatively and quantitatively conditioned by the fibre's length (compared to the characteristic lengthscales of the turbulent flow, ranging from sub-Kolmogorov to inertial subrange) (Ni, Ouellette & Voth 2014;Ni et al 2015;Pujara, Voth & Variano 2019;Oehmke et al 2021;Pujara et al 2021) and inertia (expressed by means of a representative Stokes number) (Bounoua, Bouchet & Verhille 2018;Kuperman, Sabban & van Hout 2019).…”

Section: Introductionmentioning

confidence: 99%

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On the fully coupled dynamics of flexible fibres dispersed in modulated turbulence

2022

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The present work investigates the mechanical behaviour of finite-size, elastic and inertial fibres freely moving in a homogeneous and isotropic turbulent flow at moderate Reynolds number. Four-way coupled, direct numerical simulations, based on a finite difference discretisation and the immersed boundary method, are performed to mutually couple the dynamics of fibres and fluid turbulence, allowing us to account for the backreaction of the dispersed phase to the carrier flow. An extensive parametric study is carried out in zero-gravity condition over the characteristic properties of the suspension, i.e. fibre's linear density (from iso-dense to denser-than-the-fluid fibres), length (from short fibres comparable with the dissipative scale to long fibres comparable with the integral scale) and bending stiffness (from highly flexible to almost rigid fibres), as well as the concentration (from dilute to non-dilute suspensions). Results reveal the existence of a robust turbulence modulation mechanism that is primarily controlled by the mass fraction of the suspension (with only a minor influence of the fibre's bending stiffness), which is characterised in detail by means of a scale-by-scale analysis in Fourier space. Despite such alteration with respect to the single-phase case due to the non-negligible backreaction, fibres experience only two possible flapping states (previously identified in the very dilute condition) while being transported and deformed by the flow. In addition, we show that the maximum curvature obeys different scaling laws that can be derived from the fibre dynamical equation. Finally, we explore the clustering and preferential alignment of fibres within the flow, highlighting the peculiar role of inertia and elasticity.

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Section: Resultsmentioning

confidence: 97%

Section: Preferential Alignmentmentioning

confidence: 99%

“…2021; Pujara et al. 2021) and inertia (expressed by means of a representative Stokes number) (Bounoua, Bouchet & Verhille 2018; Kuperman, Sabban & van Hout 2019).…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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On the fully coupled dynamics of flexible fibres dispersed in modulated turbulence

2022

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“…Rotation rates of complex particles have been an active field of research with applications in diverse disciplines, including the dynamics of microswimmers. Orientational dynamics of ellipsoids have revealed intricate shape-dependent orientation statistics [74,77,[93][94][95][96]. One of the main research areas scientists focus on is understanding the rotational statistics as a function of ellipsoid shape [51].…”

Section: Introductionmentioning

confidence: 99%

Physical modeling of motile and sedimenting plankton: from simple flows to turbulence

Leiva¹

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Planktonic microorganisms play a fundamental role in oceanic ecology and chemical cycles. Different planktonic species are found at various levels of the oceanic trophic chain, ranging from photosynthetic organisms to grazing species higher in the food chain. Many planktonic species have developed migration strategies to aid their survival. This includes motility and density regulation. Physical aspects, such as transport and collision rates, have a direct impact on planktonic survival and are influenced by the planktonic migration strategies. Furthermore, collision rates between planktonic organisms also play an important role in the formation of macroscopic plankton blooms. These have a direct effect on the ecology of oceans and lakes. In this dissertation we use physical modeling to study motile and sedimenting microorganisms in a fluid flow. We aim at shedding light on the key features of microorganism dynamics in fluid flows as a function of their key parameters: shape, motility, and density offset.In chapter 1 we introduce the biological setting of plankton, and give a very brief overview of the physical modeling approaches for plankton in fluid flows. Subsequently in chapter 2 we introduce the theoretical framework of turbulence and the methodology of our numerical simulations.In chapter 3 we start by examining microswimmers in a simple two-dimensional toy-model. We use methods from dynamical systems theory to uncover the role played by shape and motility in determining the microorganism dynamics in this simple setting. We explicitly identify the Hamiltonian dynamics followed by spherical microswimmers. Additionally, we find that elongated microswimmers more easily escape simple vortex structures than other shapes. In chapter 4 we then move on to ellipsoidal microswimmers in realistic mild turbulent flows. We analyze transport and rotation rates of motile ellipsoids. We find that elongated microswimmers have an advantage in transport, which is in part due to shape-dependent rotation rates. We also investigated the collision rates of motile spheres, and we were able to extract a master curve interpolating between the passive and motile limits for different sized spheres. We quantified the effect of motility and found that even very small motility greatly enhances collision rates.In chapter 5 we study of sedimentation of elongated microorganisms in mild turbulence. We measure the collision rates of elongated microorganisms in terms of size, energy dissipation rate, and aspect ratio. We then find a master curve interpolating between a passive particle and a sedimentation dominated limit. We characterize the role played by shape, which increases collision rates of elongated microorganisms in comparison with equal-volume spheres. This shape-induced enhancement helps to explain the timescales for formation of blooms of elongated planktonic species. In summary, in this dissertation we study the effect of shape, motility, and density regulation on physical models of planktonic microorganisms. Our findings help to ...

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An efficient particle tracking algorithm for large-scale parallel pseudo-spectral simulations of turbulence

Lalescu

Bramas

Rampp

et al. 2022

Computer Physics Communications

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Shape- and scale-dependent coupling between spheroids and velocity gradients in turbulence

Abstract: Abstract

Cited by 7 publications

References 53 publications

On the fully coupled dynamics of flexible fibres dispersed in modulated turbulence

On the fully coupled dynamics of flexible fibres dispersed in modulated turbulence

Physical modeling of motile and sedimenting plankton: from simple flows to turbulence

An efficient particle tracking algorithm for large-scale parallel pseudo-spectral simulations of turbulence

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